When building the transistors during the chip production in the so-called Front End of the Line (FEOL) process, it is necessary to create regions on the semiconductor wafers, in particular silicon wafers, with different doping concentrations of different elements. These different regions are the negative (n) region for which group V elements such as phosphorus and arsenic are used as the doping elements, the positive (p) region for which group III elements such as boron are frequently used, and the intrinsic (i) region with little or no doping. The doping of these regions on the semiconductor wafers are often done by the so-called ion implantation with the required elements. Moreover, other elements, e.g. carbon and fluorine, are nowadays implanted in addition. During the implantation, ions of the desired elements are massively accelerated and shot onto the semiconductor wafer in a vacuum apparatus. Due to their high velocity, they can penetrate into the crystal lattice of the semiconductor wafer and can be incorporated therein by the subsequent annealing step.
In order to allow for the formation of regions with different implantations, regions which are not supposed to be implanted by a certain type of ion have to be “shielded”. This shield is formed by a photoresist which was previously structured by a photolithographic process. Photoresist thicknesses can vary broadly in the range of several tens of nm to few μm.
However, the photoresist is not totally immune to the high velocity ion bombardment and a crust formation is observed. Besides the formation of crusts on the tops, a crust layer on the sides of the photoresist structures and at the so called footing is frequently produced. This crust formation is particularly severe when the ion implantation is done on tilted semiconductor wafers for halo ion implantation, i.e. implantation underneath the gate. Such a Crust is very difficult to remove and persists much longer than the large majority of the photoresist, especially when it is formed close to or at the photoresist/semiconductor interface. Moreover, the implantation with additional elements like fluorine yields very difficult to clean crust layers. Furthermore, low implantation energies tend to give harder to clean crusts. Their removal is particularly challenging for ultra-shallow extensions and halo regions, which are currently implemented in integrated circuit (IC) industry.
Additionally, aggressive cleaning chemistries such as SPM (sulfuric peroxide mixture) or hot sulfuric acid are capable of removing the photoresist. However, they frequently cause damage to the fragile and sensitive materials, such as silicon-germanium, germanium and high-k metals materials such as hafnium oxides, lanthanum oxide, aluminium oxide, titanium nitride or tantalum nitride, introduced into the modern transistor designs and can even attack the silicon, which leads to unwanted material loss. All in all, these disadvantageous effects lead to a decrease in performance or even to the malfunctioning of the transistors and, finally, of the whole chip. It can be foreseen that these problems and disadvantages will become even more severe with the 2X, 1X and 0X nodes to come.
Therefore, other cleaning chemistries have been proposed in the prior art.
Thus, the American patent U.S. Pat. No. 5,554,312 discloses a non-aqueous photoresist stripping composition comprising inter alia isopropanol amine (IPAM). However, it does not contain N-methylimidazole (NMI) and dimethyl sulfoxide (DMSO).
The American patent U.S. Pat. No. 6,140,027 as well as WO 2007/037628 A1 and EP 0 647 884 A1 disclose compositions including monoisopropanol amine (MIPA) and DMSO. However, these compositions do not contain N-methylimidazole (NMI).
The American patent U.S. Pat. No. 6,071,868 discloses a photoresist stripping compositions including monoisopropanol amine (MIPA) and DMSO. However, it also contains N-methylpyrrolidione (NMP).
The European patent application EP 0 647 844 A1 discloses an alkaline photoresist stripping composition comprising inter alia DMSO and 1-amino-2-propanol or 1-amino-3-propanol.
The American patent U.S. Pat. No. 6,958,312 B2 discloses a composition for removing a copper-compatible resist inter alia comprising monoisopropanolamine and N,N-dimethylimidazole, which presumably should read N,N-dimethylimidazole-1-amine.
The international patent application WO 2007/037628 A1 discloses a photoresist stripping composition inter alia comprising isopropanol amine (MIPA) and DMSO.
The international patent application WO 2010/127943 A1 discloses a resist stripping composition which is free from N-alkylpyrrolidones and contains NMI, 3-amino-1-propanol, DMSO and 1-aminopropane-2-ol as a cosolvent. The composition must contain 0.05 to <0.5% by weight, based on the complete weight of the composition, of an added quaternary ammonium hydroxide. Moreover, the composition and can contain acetylenic alcohol/alkyleneoxide adducts as surfactants.
The international patent application WO 2011/012559 A2 discloses a substantially water free post ion implant stripping composition containing 1-amino-2-propanol, DMSO and an added quaternary ammonium hydroxide. It may also contain non-ionic alkoxylated alcohols, nonylphenols and nonylethoxylates.
The European patent application EP 2 281 867 A1 discloses a semi-aqueous stripping and cleaning formulation for metal substrates containing isopropanol amine, a quaternary ammonium hydroxide and water.
The American patent U.S. Pat. No. 7,951,764 B2 discloses a Back End of the Line (BEOL) photoresist stripping and cleaning composition comprising DMSO and 1-amino-2-propanol or 1-amino-3-propanol. It may also contain dimethyl hexynol or ethoxylated tetramethyl decyndiol as a sufractant.
However, although some of the photoresist stripping and cleaning compositions avoid the drawbacks of aggressive cleaning chemistries, they do not entirely fulfill all of the strict requirements which are nowadays asked for post-implant photoresist removers in the FEOL process. In particular, the damage to the fragile and sensitive materials mentioned hereinbefore has to be reduced and the removal rates have to be improved further so that the implanted photoresists and the crusts are removed completely from the fine structures on top of the semiconductor wafers in shorter time periods than hitherto possible.